This invention relates to spray painting and more particularly to an improved vent for paint cups of the type mounted on hand held spray guns.
In one common type of hand held spray gun, paint is placed in a cup or reservoir suspended below the spray gun. The hand held spray gun is connected through a hose to a source of compressed air. When a trigger on the spray gun is squeezed, air flow through the spray gun causes a suction feed or aspiration of paint from a jar or cup into the air stream. The air stream then atomizes and discharges the paint from the gun. As paint is drawn from the cup, air must be allowed to flow into the cup to fill the space previously occupied by the paint. If air is not allowed to enter the cup, a vacuum will build up within the cup as paint is consumed until the vacuum equals the force of the suction feed, at which time no further paint will flow to the spray gun. Consequently, it is necessary to vent the cup to the atmosphere.
In the simplest type of hand held spray gun, the vent merely comprises a hole or opening in the lid or cap of the paint cup. This construction is satisfactory, provided the spray gun is not tilted during operation to a position where the vent is located below the paint surface, thereby allowing the paint to drip through the vent hole. One solution to this problem has been to provide a long, small diameter tube or passage in the paint cup cap for the vent, as illustrated in U.S. Pat. No. 2,057,434. However, a vent of this type tends to clog with paint and is difficult to clean. Certain other solutions to the problem have provided large wetted surfaces which, again, are difficult or time consuming to clean. For example, the dripping problem has been reduced by providing a vent hole on one side of the cap covering the paint cup and providing a baffle space from the cap and closing the top of the paint cup, as illustrated in U.S. Pat. No. 3,401,842. A similar vent hole is placed in the baffle, but at a location spaced from the vent hole in the cap and located to an opposite side of the spray gun. Consequently, when the spray gun is tilted, only one of the two vent holes may be located below the surface of the paint. However, if the spray gun is tilted upside down, both vent holes will be located below the surface of the paint and eventually paint will drip from the spray gun. Or, if the spray gun is tilted first to the side of the baffle vent and then to the other side, paint trapped between the baffle and the cap may leak from the cap vent.